Heating arrangement for cathodes of vacuum tubes



J. BETHENOD July 29, 1930.

HEATING ARRANGEMENT FOR CATHODES OF VACUUM TUBES Filed Sept. 5, 1923 I I Illllav INVENTOR I JOSEPH BETHENOD BY 44 ,JJQQ,

' ORNEY Patented July 29, 1930 JOSEPH BETHENOD, OF PARIS, FRANCE HEATING ARRANGEMENT FOI, CATHODES F VACUUM TUBES Application filed September 5, 1928, Serial No. 661,108, and in France September 19, 1922.

It is known that the. filament forming the cathode of an electron tube, such as a triode, may be heated by means of alternating currents of more or less high frequencies. This heating arrangement is often of great prac tical benefit particularly as far as the current source is concerned. However, the arrangement has serious drawbacks when the triodes are used for amplifying or detecting in wire less telegraph and particularly wireless telehone stations. As well-known, the Joule etiect in the lilament is always in proportion with the square of the current and it annuls itself twice per period. As a result of this, the temperature of said filament varies also in a pulsatory manner, the mass of the heated metal being always relatively small.

The invention may be more clearly understood by referring to the following detailed description which should be read in connection with the accompanying drawing in which:

Fig. 1 shows a vacuum tube conforming to the invention, and,

Fig. shows a modification thereof.

Referring to Fig. 1, the reference numeral 1 designates the base and G the globe of the vacuum tube. The anode 5 consists of a hollow metallic cylinder supported in the pres ent case by its lead-in conductor which is sealed through the flare 2. The grid 4: consists of a spiral wire likewise supported by its leadin conductor. The filamentary cathode, which may be heated from any multi-phase source of current, is shown in the drawing as arranged for excitation from a three-phase source of current, and in this instance consists of three spirals of wire 3 supported by their lead in wires and symmetrically disposed with respect to each other as generatrices of a cylinder. The upper ends of these spirals are connected together as shown, formin When these spirally Wound cathode filaments are energized by three'phase currents they will emit electrons in the usual manner but owing to the three phase connection there will be no zero point of electron emission. In other words, one or more of the filaments will always be emitting electrons when the plate is a three phase star connection' in operation, thereby giving a substantially steady How of electrons in spite of the use of alternating current as cathode heating means.

Figure 2 shows a modification in which the base I1, globe l6, anode and grid 14 are the same as in Fig. l. The cathode however, consists of a hollow metallic cylinder 18 enclosing the heating filaments 17 which may be connected in a manner, entirely similar to the cathode filaments of Fig. 1. In this case the 50 electrons. The cylinder 18 may be activated either by heat radiation from the spirals 17 or by electronic bombardment or a combination of the two.

- The electronic emission comprises therefore snllicient pulsations to insure that the tele- 7e phonic apparatus be the seat of a fairly sharp continuous tone which is very annoying in the receiving. In accordance with the present invention, the heating is effected by means of polyphase currents by replacing the usual single filament with a suitable number of filaments respectively traversed by current of a phase. The cathode thus constituted will, therefore, always have a strongly heated portion, the total Joule effect remaining prac so tically constant. In this manner the amplitude of the pulsations of-electronic emision is considerably reduced.

In the usual triodes in which cylindrical anodes and grids are provided, the multiple filaments maybe regularly arranged as generatriecs of a cylinder and will comprise a common metallic connection at one end (star connection). In accordance with a known principle, the cathode proper may consist of a supplementary metallic cylinder, surrounding said filaments which indirectly heat it by radiation or by an electronic bombardment of the inside surface. It should be understood that in case of monophase current this current may be transformed into polyphase current by means of any Well known arrangement and particularly by the arrangements used for the control of monophase induction motors. I201: example, the

heating may be by two-phase currents by means of two parallel filaments with a connection at one end serving as a common return path.

Finally, the heatingarrangement forming the object ofthe present invention is applicable also to high frequency current generating triodes.

Having described my invention, what I claim is:

1. In a vacuum tube, means for heating a hollow cathode by alternating current 1ncluding a plurality of filaments disposed within the cathode and adapted to be ener- 'zed from a polyphase source of current, whereby the cathode is maintained at substantially constant temperature.

2. A thermionic device comprising an anode, a control electrode positioned within said anode, a cathode positioned Within said control electrode, a plurality of filaments symmetrically arranged within said cathode, and connections for heating each of said filaments from a separate phase of polyphase current whereby a constant heating effect; is applied to said cathode.

3. A space discharge device comprising an evacuated vessel, an anode, a control electrode and a cathode positioned within said vessel a plurality of filaments for heating said cathode, and leads for connecting each of said filaments to a separate phase of polyphase current, whereby a constant heating efiect is provided for said cathode.

JOSEPH BETHENOD. 

